A rotating electric machine used to drive a vehicle needs to rotate at a speed higher than the speed at which a standard rotating electric machine typically rotates in a different application and therefore, it is crucial that the rotor thereof achieve a sufficiently high level of strength. It is particularly important to assure a high level of strength over the area where the rotor core is fastened to the rotating shaft member. While the rotor core and the rotating shaft member constituting a rotor in the related art are often fastened together by using a clearance-fitted key, there is a concern that stress tends to concentrate readily at the key.
This issue is addressed in patent literature 1, disclosing a rotor that includes a recessed part at the key, which assumes a shape achieved by forming, continuous to each other, at a key side surface, a circular arc part having a first radius of curvature and a circular arc part having a second radius of curvature greater than the first radius of curvature, so as to reduce the extent of stress concentration.
However, a stress reducing effect greater than that disclosed in patent literature 1 is sought in order to meet the increasing need for improved rotating electric machine performance. The rotating electric machine disclosed in patent literature 2 is characterized in that the contour of a notch located at the base end of the key includes a first R (round) part extending from the key base end, a straight part extending from the first R part along a direction perpendicular to a key side end, a second R part extending from the straight part and a transition part extending from the second R part to the inner edge of a through hole formed in a core plate.